1. Field of the Invention
This invention relates to a new food additive or animal feed that may be made from thermochemically hydrolyzed, solvent-extracted corn fiber hulls.
2. Description of the Background Art
Corn fiber is produced by corn wet-milling at the rate of about 13% per bushel of corn processed. More than approximately 15,000 tons of corn fiber are produced per day at wet-mills according to the Corn Refiners Association. Along with the corn fiber, portions of the protein, oil, and starch from corn are separated with the fiber stream, and when combined with corn steep liquor and stillage that are sprayed on the fiber along with corn germ meal, which is mixed into the stream, a total of about 25% of the corn processed becomes part of the corn gluten feed stream. Corn steep liquor is the liquid that is derived from the initial steeping of the corn kernels, and stillage is the bottoms from the distillation of the ethanol fermentation broth.
The corn steep liquor and stillage provide nutrients and protein to the corn gluten feed, which is a low value by-product stream that is sold as animal feed. It is desirable to obtain higher value streams from this relatively low value stream. In the present invention, the corn fiber stream, which has been processed to separate higher-value products, such as phytosterol-containing corn fiber oil, can be utilized as a food additive or a digestible animal feed. The invention also covers the fiber produced by the process and uses of this fiber as a food additive. The invention also includes the animal feed produced by the process, and any animal feed with similar properties.
Corn fiber is composed of approximately 15-25% starch, 10-13% protein, 33-42% hemicellulose, 15-18% cellulose, 3-6% ash, 3-6% oil, and 1-2% other components. The hemicellulose is composed of about 50-55% xylose, 30-35% arabinose, 4-6% galactose, 3-5% D-glucuronic acid and 2-5% other components including mannose, coumaric acid, and ferulic acid. In an exemplary hydrolysis process, a corn fiber stream coming from dewatering presses contains about 30 to about 50% solids. During thermochemical treatment of the corn fiber, the fiber is heated to about 138 to about 190° Centigrade (C), which solubilizes the starch and hemicellulose fractions, while leaving the cellulose intact. Starch is composed of two types of glucose polymers, amylose and amylopectin. Amylose is a linear polymer with the glucose molecules linked by α-1,4-glycosidic bonds, and amylopectin is a highly branched polymer with the glucose molecules linked by α-1,4-glycosidic bonds with α-1,6 linked branches. Hemicellulose in corn fiber is composed of a β-1,4 linked xylose backbone with side-chains composed of arabinose, xylose, glucose, galactose, mannose, glucuronic acid, ferulic acid, and coumaric acid.
The starch can be removed from the fiber by hydrolysis with a combination of heat and either starch-degrading enzymes or sulfuric acid. Under these conditions, the starch polymer is hydrolyzed first to soluble oligosaccharides, which can be further hydrolyzed to glucose by a secondary acid or enzyme hydrolysis step. The hemicellulose can be partially hydrolyzed by treating the corn fiber at temperatures above 121° C., but the complete hydrolysis of the xylan backbone to monomers requires the presence of acid or enzymes.
The hydrolysis of the starch and the hemicellulose can also be combined into a single step. The native corn fiber, containing residual sulfur dioxide from the steeping process, can be treated at high temperatures with the optional addition of acid. This treatment will cause simultaneous hydrolysis of the starch and the hemicellulose.
The monosaccharides from the hydrolyzed starch and hemicellulose can be used in many different industrial applications, including fermentations and catalytic conversion to sugar alcohols and subsequently polyols. The glucose from the starch can be used in a yeast fermentation to produce ethanol, or can be fermented to other products. The xylose can also be similarly fermented to a number of fermentation-derived products known by those persons skilled in the art. The ferulic acid can be used as a feedstock for the production of vanillin.
3. Definitions
As used herein, “wet-milling” is a process by which corn can be converted into ethanol, corn sweeteners, and starches.
As used herein, “corn fiber” is the product obtained from the wet-milling process, which involves an initial steeping of corn kernels in aqueous sulfur dioxide at an elevated temperature followed by gentle grinding and physical separation of the outer fiber layers from starch, protein and other components.
As used herein, “corn steep liquor” is a liquid that is derived from the initial steeping of the corn kernels in wet-milling.
As used herein, “stillage” is the bottoms from the distillation of an ethanol fermentation broth in a wet-milling process.
As used herein, “corn gluten feed” is a relatively low value by-product stream of the wet-milling process that is sold as animal feed
As used herein, “phytosterols” include, for example but are not limited to, beta-sitosterol, sitostanol, campesterol, campestanol, stigmasterol, stigmastanol, brassicasterol, and other compounds containing the sterol ring system.
As used herein, “total sterols” include, for example but not limited to, all of the phytosterols described herein. As used herein, phytosterols also include sterol glucosides, sterol fatty acid esters, and sterol ferulate esters.
As used herein, “high solids content” means a corn fiber slurry having a moisture content from about 20 weight percent to about 50 weight percent solids.
As used herein, “acid detergent fiber” (ADF) is the percentage of plant material in a feed or forage insoluble in an acid detergent solution, (equivalent to AOAC method 973.18). Generally, the lower the ADF the more digestible a feed is to an animal.
As used herein, “acid detergent insoluble crude protein” (ADI-CP) is nitrogen remaining in acid detergent fiber residue. ADI-CP is generally considered to be an estimate of heat damage occurring during storage and processing.
As used herein, “neutral detergent fiber” (NDF) is the percentage of cell wall material or plant structure in a feed. The lower the NDF percentage, the more an animal will eat. NDF includes acid detergent fiber and is inversely related to intake, therefore, a low percentage of NDF is desirable.
As used herein, “neutral detergent insoluble crude protein” (NDI-CP) is nitrogen remaining in neutral detergent fiber residue.
As used herein, “lignin” is a biologically unavailable mixture of polymers of phenolic acid. Lignin is generally recognized as a major structural component of mature plants and trees.
As used herein, “relative feed value” (RFV) is a measure of feed value compared to full bloom pure alfalfa, where 100 is equal to full bloom alfalfa, and an RFV above 100 indicates a feed value greater than that of full bloom alfalfa.
As used herein, “net energy for gain” (NEG) is an estimate of the energy of feed available for the deposition of body tissue in non-lactating animals.
As used herein, “net energy for maintenance” (NEM) is an estimate of the energy of feed available for the maintenance of non-lactating animals.
As used herein, “net energy of lactation” (NEL) is an estimate of energy in feed available for body maintenance and milk secretion.
As used herein, “total digestible nutrients” (TDN) is the sum of the digestible protein, digestible nitrogen free extract, digestible crude fiber, and the digestible fat. TDN accounts for fecal loss of digestion and to some extent the urinary energy loss.
As used herein, “nitrogen free extract” (NFE) is the highly digestible portion of a plant, comprised mostly of carbohydrates. NFE is often viewed as what remains after the protein, ash, crude fiber, ether extracts, and moisture content have been obtained.
As used herein, “nonstructural carbohydrates” (NSC) are starches and sugars that serve as energy sources for the feed recipient.
As used herein, “adjusted crude protein” (adj. c. protein) is crude protein corrected for insoluble crude protein.